For example, a cylinder block constituting an engine has a space (hereinafter referred to as “a first space”) consisting of a crankcase in which a crankshaft is stored, cylinder bores and the like, a space (hereinafter referred to as “a second space”) through which cooling water flows, and a space (hereinafter referred to as “a third space”) through which engine oil flows.
In order to secure an engine function, a fluid flowing through each of these spaces formed in the cylinder block should not leak (causes leakage) to the other spaces.
However, if a cylinder block has a defect such as a blow hole, the blow hole forms a route which connects the spaces and therefore leakage may occur between the spaces and the outside.
Conventionally, a workpiece such as, typically, a cylinder block or a cylinder head including three partitioned void portions is inspected whether or not leakage occurs in the first to third spaces (i.e., a leak test is conducted), and then is supplied to a next process.
Moreover, various techniques of precisely conducting such a leak test are studied. For example, such a technique is disclosed in JP 2000-121485 A, and is publicly known.
The conventional technique disclosed in JP 2000-121485 A is configured to conduct a leak test of a workpiece including spaces of a plurality of systems (e.g., three systems), the leak test including calculating an alternative characteristic value of a flow path resistance based on a change in a flow rate and a change in a pressure in charging pressure, and evaluating this alternative characteristic value to determine whether leakage occurs or not.